ovens and efficiency

Dear Oven builders, mud teachers, bakers, and eaters:

I would like to talk to you about some of the claims being published about the efficiency of earthen ovens.

I think we need to be clear that any masonry oven, whether it’s made of unfired earth or fired brick, is not, by definition, a “fuel efficient appliance” – especially if it isn’t insulated.

There are more and less efficient ways to work with an oven, and some of them make quite good use of the wood burnt in them, but in my experience, those ways don’t apply to people who just want to cook a few pizzas, or a few loaves of bread, or perhaps a holiday turkey. That kind of use requires the burning of many pounds of fuel to cook just a few pounds of bread or meat. I don’t think we can call that “fuel efficient.”

There are different kinds of efficiency besides fuel efficiency, and those are, I think, equally important. “Efficiency” itself means “what comes of our making,” and goes far beyond pounds of food cooked for pounds of fuel burnt. There is also the work of making family and community, which can benefit greatly from the kind of communal hearth provided by an oven. There is the work of building relationships with each other and the earth, which can benefit greatly from working together with strangers to build something beautiful and useful. Ovens can be wonderful even when they go unfired: simple and magical to build, lovely to look at, and beautiful for how they bring people together. But like every thing human — like every thing living — life comes at the cost of life — and in order to actually cook in your oven, the cost is the life of trees that we cut and burn as firewood.

I suspect that most of the ovens built in the US don’t get used more than a few times a year, and if they bring people together for a day or even just a few hours, then perhaps the exchange of life for life is fair. If they are well insulated and fired with small dry sticks, the exchange is even better (good insulation under the hearth and over the dome can increase retention of useful baking temps from just a few hours to 12 or more).

But when we teach people to build ovens, or if we build ovens for clients, I think it’s very important to be very clear that the simple /fuel efficiency/ of an oven can be anything from terrible (a few pizzas) to OK (pizzas, flatbread, loaf bread, meat, casseroles, lasagna, soup, pies, stew, cookies, warmed milk for yogurt, dried food, and dry wood for the next firing). In America, we are rich enough in fuel that we don’t pay that close attention to how many trees we cut to cook our food — but that is not so in many other countries. So a claim of “efficiency” in America or on the web may carry the wrong message to a country where trees are scarce, and fuel is in short supply.

If you’re interested, I’m happy for a chance to continue this discussion, either here on the blog site, through the comment option, or directly (contact me at handprintpress.com, or by snail mail at POB 576, Blodgett OR 97326).

About Kiko Denzer

I live in western Oregon with my family. Hand Print Press is our small part of a collaborative project that tries to restore the arts of living to their rightful, traditional, public role, as a medium for growing human culture. The web is a poor substitute, but if it can help some of us find each other -- good!

8 Responses to ovens and efficiency

  1. Angela says:

    Hi,I’m slowly dignsieng my house, to be built by me. It’ll be on one of the gulf islands in British Columbia, Canada.I love the whole concept of the Kachelofen.However, due to economic constraints, I’d like to build it myself. If supplied with a floor-plan, square footage etc. would you design a stove for me and if so, at what cost?Thank you very much.ak

  2. Vicki says:

    Hello Kiko: Although these ovens are not ‘efficient’, I am entertained by how much one can cook/bake with one firing. When I am most organized, a three hour burn will be enough to start out with pizzas, then go to a couple loads of bread, then can cook any items for dinner, ie. meant, roasted vegetables, whole squash, etc. Then we can put in vegetables or herbs to dry and even a couple apples that will be still warm in the morning. Ours can be at the center of some of our educational programs . . collecting wood, building fire, fire safety, harvesting, grinding, fermenting grains, baking birthday cakes, bread, pizzas. . . storytelling, artistic work. . .

    Will you be giving any public bread oven workshops in the summer time? Thank you, Vicki

  3. kikodenzer says:

    John,

    I’ve not heard that particular assessment of kitty litter — and tho I do understand that it’s made of clay, I’ve not used it for oven building — sounds like a good experiment. (I do suspect that brands vary quite a bit depending on where they source their clay, and how they treat it — or not.)

    My solution to the problem of crumbling inner layers has been to soak them with a mix of half water and half “waterglass,” aka sodium silicate; it is used by potters to deflocculate glazes, and to mend kilns. At high temps, it fuses w/surrounding aggregate and helps hold stuff together. Available at ceramic suppliers. It’s also caustic, so take appropriate precautions.

    Also, if you “mist” your loaves, or squirt water into the oven to aid crust development, it will take a heavy toll on the interior surface. Alan Scott always maintained that true hearth loaves steamed themselves with water from the dough — I agree with that, and like the loaves we make without spraying.

    I do use a damp scuffle to clean the oven floor, but I don’t make it dripping wet. Since the steam generated by the mopping is truly steam, it produces less thermal shock to the oven dome than drops of actual water (remember that converting water to steam requires substantially more energy than simply raising the temperature of water one more degree).

    All clay will degrade with repeated thermal shock, even the finest firebrick.

    If you try the kitty litter approach, do take notes and share what you learn!

    You might also ask on the brickoven listserve at yahoo.groups.

    Hope this helps. And that you have a lovely winter/solstice/xmas there in VT.

    Best,

    — Kiko

  4. kikodenzer says:

    Jonathan,

    I’ve read The Book of Masonry Stoves, and recommend it highly to anyone interested in building an indoor oven — it’s a very good solution in places where climate and budget go that way. I’ve also built masonry heaters of the rocket stove variety (which can be modified to bake as well), so I certainly appreciate your point and agree completely. Maybe we need a new book that combines some of these stories and principles?

  5. A well researched site, I’ll link to it from my site thanks

  6. Jonathan says:

    Kiko, I don’t know what claims are being made for masonry ovens with regard to their energy efficiency in cooking food. But sometimes people refer to masonry heaters as masonry “ovens” whether or not they include an actual built in oven feature, separate from the burning chamber. (Our own book here at Chelsea Green helps to spread this confusion, being called “The Book of Masonry Stoves” when “…Masonry Heaters” would be the actually and technically correct term. But the book is many years old, so it’s too late to change the title.)

    A masonry oven fired up just to cook one meal will be energy inefficient, as you say. But a masonry heater that is fired up to heat your home in the winter can be fantastically efficient, and that’s even before you cook food in the oven compartment that might be included without having to burn any additional fuel. Some of these masonry heaters will keep a sizable home warm all day with just a small amount of wood burned. And the bread that might come with the process is a fantastic frosting on the cake.

    Of course we have to be sure we’re talking about the same things here. One day, hopefully everyone will know the difference between a masonry heater and a masonry oven, and will use the terms accurately to avoid confusion.

  7. Kiko, I am a happy reader of your “Earth Oven” book, and builder/user of an oven based almost exactly on the model design in your book. I’ve also consulted with another reader on her own build of your design. We use it mostly for pizza parties, and our family and friends have enjoyed many over the past three years!

    Thanks very much for your comments above; I’ve often felt that one must have a holistic view of the oven making enterprise, from gathering the materials, to construction, to gathering fuel before each firing, to the firing and cooking. For each firing I get my guests involved, and I guarantee it makes everything taste better!

    Here’s a question: I used the “Vermont Grey” clay that we have so much of around here and it seemed to work well, but I think my current oven reached it’s end-of-life this year as bits of the interior started falling in. Frankly this was a minor problem from the beginning, but really only started happening during firing after three years; this is bad when my focus is pizza!

    When I build again next spring, I wonder if there is something I can do when I build the “lining” (the inner layer) do make it a bit more “refractory.” I’ve heard for example that dissolving kitty litter creates the equivalent of refractory cement; wondering if you’ve heard of that.

    Thanks very much for your great book!!!

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